You are thinking of DNG which is more of a container format. It can use multiple image formats internally to record the actual image, one of them being JPEG-XL.

iPhone raw images are actually a jpeg xl inside the DNG.

True. I would love to have lossless images (and video) out of my devices still. Not as a replacement for RAW but as a middle ground between RAW and lossy JPEG.

Not for quality reasons primaily but because keeping the first stages of the processing pipeline and the archival branch lossless solves some headaches.